The invention relates to a connection system for releasably coupling a first body (5) with a flange (25) to a fluid-conducting system in a force-fitting manner, and the invention also relates to a connection system for releasably coupling the interior of a first fluid-conducting body (5) to the interior of a second fluid-conducting body (3) in a force-fitting manner. The second body (3) has a second end with a circumferential wall (22), a membrane contact portion (9) which can be found on the wall, and an opening (43). A retaining element (2) has a passage (35) and a peripheral outer edge (24). One side and/or the passage (35) of the retaining element (2) is coupled to the membrane (1), and an annular wall (26) is arranged on the same side, said annular wall being connected to the circumferential wall (22) of the second body (3). The other side is designed to contact the surface of the flange (25) of the first body (5). The retaining element (2) can also be integrated into the second body (3) when the first body (5) is fluid-conductive. The releasable connection element (4) is designed to at least partly surround the peripheral outer edge (24) of the retaining element (2) and the flange (25) of the first body (5).
